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28.09.2011

Rh(I)-catalyzed [2+2+2] cycloaddition reactions: experimental and theoretical studies

Prof. Dr. Anne Roglans (Universitat de Girona, Spanien)
Kleiner Hörsaal, 11:00 Uhr

Abstract: Transition-metal catalyzed cycloaddition reactions have become one of the preferred tools for organic chemists due to their capacity to generate cyclic systems with high structural complexity from simple precursors. The metal-catalyzed [2+2+2] cycloaddition reaction is among the most useful of this group of transformations, allowing the preparation of a variety of synthetically valuable carbo- and heterocyclic six-membered rings starting from different unsaturated substrates.

For some years now our group at the University of Girona has been interested in the development of the Rh(I)-catalyzed [2+2+2] cycloaddition reaction. Initially, the focus of our research was on an application of this reaction type to the synthesis of polyunsaturated macrocycles as first examples of a completely intramolecular [2+2+2] cycloaddition in a closed system. The cycloisomerization of an array of polyunsaturated azamacrocycles catalyzed by Rh(I) complexes allowed us to efficiently synthesize fused tetracyclic benzene derivatives starting from triyne macrocycles and fused tetracyclic 1,3-cyclo¬hexadienes when we started with enediyne macrocycles. Apart from the methodological interest, we were challenged by the mechanistic aspects of the [2+2+2] cycloaddition, so we undertook DFT calculations which helped us to explain both the reactivity and the regioselective outcome of this process. Parallel, we have also applied this powerful transformation to the synthesis of new non-natural aminoacids and to the preparation of fused polycyclic pyridines and bipyridines